Optimizing NH₄⁺ Storage Capability of Nickel Ferrocyanide by Regulating Coordination Anion in Aqueous Electrolytes

Abstract

Will anions in electrolytes affect the electrochemical properties of Prussian blue analogues for aqueous ammonium ion batteries? In this study, the electrochemical reaction between nickel ferrocyanide and ammonium ions is investigated in three common inorganic ammonium salt solutions [NH4NO3, NH4Cl, and (NH4)2SO4]. The results suggest that at the same NH4+ concentration, nickel ferrocyanide exhibits different electrochemical performances. The as‐prepared nickel ferrocyanide contains two phases, which are rhombohedral phase and cubic phase. Rhombohedral phase of nickel ferrocyanide has a high reactivity in 0.5 M (NH4)2SO4 solution during cycling while cubic phase shows good performance in 1 M NH4NO3 and 1 M NH4Cl electrolyte. It should be noted that the performance of cubic phase is superior to rhombohedral phase in kinetic consideration. Additionally, due to the strong coordination ability of chloride, nickel ferrocyanide exhibits an excellent electrochemical performance in 1 M NH4NO3 solution, rather than 1 M NH4Cl electrolyte.

Ammonium Ion Batteries: Material, Electrochemistry and Strategy

“…The size of the channels in PBAs is about 0.32×0.32 nm, which is larger than the ionic radius of NH 4 + (0.154 nm) [95] . It indicates that NH 4 + can rapidly diffuse in such 3D structure [96–100] . During the NH 4 + insertion process, hydrogen bonds are formed between the hydrogen atom in NH 4 + and nitrogen atom in PBAs framework.…”

“…[95] It indicates that NH 4 + can rapidly diffuse in such 3D structure. [96][97][98][99][100] During the NH 4 + insertion process, hydrogen bonds are formed between the hydrogen atom in NH 4…”

A salt-concentrated electrolyte for aqueous ammonium-ion hybrid batteries

“…Aqueous ammonium-ion batteries (AAIBs) using non-metallic ammonium ions (NH 4 + ) as charge carriers are receiving increasing attention, due to the fast diffusion kinetics of NH 4 + and the interesting H-bonding chemistry between NH 4 + and host materials. [1][2][3][4] Current research in AAIBs mainly focuses on fabricating high-performance electrode materials, such as metal oxides, [5][6][7][8][9] polyanionic compounds, 10 conducting polymers, 11,12 Prussian blue analogues, [13][14][15][16] etc. Yet, the systematic study of electrolytes which are compatible with these NH 4 + hosting materials is still lagging, limiting the development of competitive AAIBs.…”